Hong Kong, once the world’s busiest cargo port, has dropped to fifth place after 18 months of steadily declining volume. Year-over-year declines reached a staggering 12.8% in October 2015.

Though China’s slowdown has shrunk overall global trade, Hong Kong’s tenuous position is unique. The former British outpost was once the gateway to China, but it now has fierce competition on the mainland. The port at Shenzhen has seen growing volumes over the same period, and both Shenzhen and Shanghai are now busier than Hong Kong.

Hong Kong was initially an attractive holding for the British because of its large natural harbor. Over the 20th century, logistics and trade have come to make up nearly a quarter of the city’s economy, and the loss of port traffic would be devastating. Critics say local administrators have been too slow in reacting to the massive shift, making it less likely there will be enough big moves for the port to regain its prominence – or even, more realistically, to keep from slipping further from the center of world trade.

The decline seems set to continue with Deutsche Bank recently finding that Hong Kong’s volume could drop by as much as half over the next decade.

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The multiple forces causing the collapse seem stubborn, if not insurmountable. Fundamentally, trade growth in China makes direct routes more attractive. Mainland Chinese ports have also surpassed Hong Kong’s ability to serve the very large ships in the Asia-Europe trade. Though Hong Kong is dredging its channel and harbor to accommodate the new generation of megaships, there is still a relative lack of space for offloading cargo.

Mainland port fees are also now as much as 30% cheaper for carriers than Hong Kong. There’s even a strange bureaucratic hurdle in the mix: truck drivers from the mainland are not allowed to drive into Hong Kong to pick up or deliver cargo.

Even more foreboding was Deutsche Bank’s finding that many shippers who do still ship via Hong Kong found the greatest benefit from its connectivity. Its legacy status as a prominent network node, with more frequent arrivals and higher volume of ships, makes it easier to arrange multi-stage cargo routes.

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But looking forward, that’s a weakness, not a strength. As fundamentals drive shippers to other ports, each lost connection weakens Hong Kong’s network advantage, creating a downward spiral—something like the mass defections that have impacted social networks like MySpace.